In multilayer packaging, various layers are often combined to provide a final product that has the characteristics of the separate layers. For example, structures that include different types of polyethylene, polypropylene, and ethylene vinyl acetate together with barrier layers such as ethylene vinyl alcohol (EVOH) and polyamide (PA) are often used in food packaging applications for meat and cheese. In such multilayer constructions, polypropylene typically provides stiffness, temperature resistance and scuff resistance. Polyethylene typically provides clarity and tear resistance, seals at a lower temperature and is softer than polypropylene. Styrene polymers can be included in such structures to provide structural integrity. Although it is possible to use a blend of polypropylene and polyethylene in a single layer, in conjunction with barrier and styrene polymer layers, the blend layer will not provide the full performance of a structure containing separate layers of polypropylene and polyethylene. However, a challenge presented by the design of multilayer structures is adhering the separate layers. This is particularly the case for structures containing both polypropylene and polyethylene layers, and also styrene polymer layers in thermoforming applications. It is desirable to utilize a single tie layer in a multilayer structure, otherwise in a commercial setting, capital investment would thus be required for multiple extruders, and additional extrusion steps translate to higher operating costs.
U.S. Pat. Publ. 2007/0167569 discloses adhesives containing styrene-isoprene-styrene polymers in multilayer structures containing styrene polymer layers. U.S. Pat Publ. 2009/0171022 discloses adhesives containing styrene-isoprene-styrene/styrene-butadiene-styrene polymer blends in multilayer structures containing styrene polymer layers. U.S. Pat. No. 6,184,298 discloses adhesives containing unmodified styrene-based elastomers in multilayer structures containing polyethylene and polypropylene. However, a continuing need exists for multilayer structures containing layers of polyethylene, propylene polymers, and styrene polymers, having a common tie layer with the capability of adhering all layers in the structure.